This patent application claims priority based on a Japanese patent application, H11-010023 filed on Jan. 19, 1999, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention is related to an optical fiber heat treatment method that can treat the surface of an optical fiber base material evenly by a flame, and an optical fiber manufacture method using said heat treatment method.
2. Description of Related Art
An optical fiber is manufactured from an optical fiber base material as the raw materials. Principal ingredient of an optical fiber base material is quartz glass. An optical fiber base material is heated and elongated to the predetermined diameter to be an optical fiber preform. An optical fiber preform is drawn to be an optical fiber.
If there are some damages and unevenness in the surface of an optical fiber base material, an optical fiber will be cut off during drawing the optical fiber base material to an optical fiber. Also, the ratio between core diameter and cladding diameter of the optical fiber become uneven. If impure foreign substances are attached to the surface of the optical fiber base material, quality of the optical fiber will be decrease. Furthermore, if residual strain inside an optical fiber base material is large, crack is caused with small impact during drawing or transporting of the optical fiber base material.
Therefore,. the surface of an optical fiber base material is prefer to be even and without impure foreign substances. Also, residual strain inside an optical fiber base material is prefer to be small. A flame polishing is usually performed to remove damages of the surface of an optical fiber base material and residual strain inside an optical fiber base material. The flame polishing heats the surface of the optical fiber base material to about 200xc2x0 C. by a burner with rotating the optical fiber base material.
However, in this temperature, a part of quartz glass SiO2 on the surface of an optical fiber base material is dissociated and becomes SiO. Therefore, the part of quartz glass SiO2 is dispersed. SiO connects with the oxygen in the atmosphere, and becomes glass particles once again. Then, glass particles are attaches near the part of the surface of the base material heated by flame and clouds the surface of the base material.
This cloud can be removed by heating the base material with weak flame. But if heating isn""t sufficient, strain remains inside the base material. Conversely, if heating is more than it is necessary, cloud will be occurred once again.
It is an objective of the present invention to provide an optical fiber heat treatment method and an optical fiber manufacture method used the heat treatment method to solve the problems above. The optical fiber heat treatment method can remove damages, unevenness, and unevenness cased by impure foreign substances of the surface of an optical fiber base material, residual strain inside an optical fiber base material, and cloud caused by the attachment of glass particles.
The optical fiber base material heat treatment method can be provided that the first flame polishing heats the surface of the optical fiber base material with flame while keeping a length of the optical fiber base material constant and the second flame polishing heats the surface of the optical fiber base material with flame by lower temperature than the temperature of the heating of the first flame polishing.
The optical fiber base material heat treatment method can be provided that the first flame polishing removes uneven parts of the surface of the optical fiber base material by the heating.
The optical fiber base material heat treatment method can be provided that the second flame polishing removes residual strain inside the optical fiber base material and cloud of the surface of the optical fiber base material by the heating.
The optical fiber base material heat treatment method can be provided that the first flame polishing at least heats locally uneven parts of the surface of the optical fiber base material, and the second flame polishing heats entire surface of the optical fiber base material.
The optical fiber base material heat treatment method can be provided that the first flame polishing heats the optical fiber base material so that the temperature of the surface of the optical fiber base material becomes approximately between 1800xc2x0 C. and 2200xc2x0 C.
The optical fiber base material heat treatment method can be provided that the second flame polishing heats the optical fiber base material so that the temperature of the surface of the optical fiber base material becomes approximately between 1000xc2x0 C. and 1800xc2x0 C.
The optical fiber base material heat treatment method can be provided that the flame is generated by burning combustible gas, which contains hydrogen, and supporting gas, which contains oxygen for supporting combustion.
The optical fiber base material heat treatment method can be provided that the flame is generated by burning combustible gas, which contains chain hydrocarbon, and supporting gas, which contains oxygen for supporting combustion.
The optical fiber base material heat treatment method can be provided that the first flame polishing heats the surface of the optical fiber base material with flame while keeping a length of the optical fiber base material constant, the second flame polishing heats the surface of the optical fiber base material with flame by lower temperature than the temperature of the heating of the first flame polishing, and drawing the optical fiber base material to filament-like form by heating the optical fiber base material generates the optical fiber.
The optical fiber manufacture method can be provided that the first flame polishing removes uneven parts of the surface of the optical fiber base material by heating.
The optical fiber manufacture method can be provided that the second flame polishing removes residual strain inside the optical fiber base material and cloud of the surface of the optical fiber base material by heating.
The optical fiber manufacture method can be provided that the first flame polishing at least heats locally the uneven parts of the surface of the optical fiber base material, and the second flame polishing heats entire surface of the optical fiber base material.
The optical fiber manufacture method can be provided that that the first flame polishing heats the optical fiber base material so that the temperature of the surface of the optical fiber base material becomes approximately between 1800xc2x0 C. and 2200xc2x0 C.
The optical: fiber manufacture method can be provided that that the second flame polishing heats the optical fiber base material so that the temperature of the surface of the optical fiber base material becomes approximately between 1000xc2x0 C. and 1800xc2x0 C.
The optical: fiber manufacture method can be provided that the flame is generated by burning combustible gas, which contains hydrogen, and supporting gas, which contains oxygen for supporting combustion.
The optical fiber manufacture method can be provided that the flame is generated by burning combustible gas, which contains chain hydrocarbon, and supporting gas, which contains oxygen for supporting combustion.